Advanced Foundation Engineering Rr420101

Set No. 1

Code No: RR420101

IV B.Tech II Semester Regular Examinations, Apr/May 2007 ADVANCED FOUNDATION ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Discuss in detail the Meyerhof’s bearing capacity theory. (b) Determine the ultimate bearing capacity of a square footing 2m × 2m in a soil with unit weight of 18 kN/m3 , ∅= 250 , c= 20 kN/m2 . Take the depth of foundation as 1.8m, Use Hansen’s equation. For ∅= 250 , Nc = 20.7, Nq = 10.7 and Nγ = 8.1. [10+6] 2. What is total settlement of a foundation? Discuss in brief various methods of estimating the total settlement of a foundation. [16] 3. How would you estimate the settlement of pile groups in (a) cohesionless soils, (b) cohesive soils?

[16]

4. (a) Write a note on multi under-reamed pile. (b) A square pile group of 9 piles passes through a recently filled up soil. The depth of fill =3m. The diameter of pile is 300 mm and they are spaced at 90cm apart. If the soil is cohesive with qu = 60kN/m2 , γ = 15kN/m3 , compute the negative skin frictional load on the pile group. [8+8] 5. (a) What are the advantages and disadvantages of Pneumatic Caisson over open Caisson? (b) A circular well has an external diameter of 7.5 m and is sunk into a sandy soil to a depth of 20 m below the maximum scour level. The resultant horizontal force is 1800 kN. The well is subjected to a moment of 36,000 kN-m about the maximum scour level due to the lateral force. Determine whether the well is safe against lateral forces, assuming the well to rotate i. about a point above the base, and ii. about the base. Assume γ ′ = 10kN/m3 , and ∅ = 320 . Use Terzaghi’s analysis and a factor of safety of 2 against passive resistance. [8+8] 6. What are anchored bulk heads? Describe the method of analyzing anchored bulk head with free- earth support in different soils. [16] 7. (a) Explain how expansive soils are formed in nature and discuss the structure of montmorillonite clay mineral 1 of 2

Set No. 1

Code No: RR420101

(b) Explain the clay mineral identification by various methods.

[8+8]

8. When are under-reamed piles used? Analyse a typical under-reamed pile and give the various design implications. [16] ⋆⋆⋆⋆⋆

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Set No. 2

Code No: RR420101

IV B.Tech II Semester Regular Examinations, Apr/May 2007 ADVANCED FOUNDATION ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) How would you determine the contact pressure for a footing subjected to loads placed eccentrically placed? (b) Compute the ultimate load that an eccentrically loaded square footing of width 2.1m with an eccentricity of 0.35m can take at a depth of 0.5m in a soil with γ= 18 kN/m3 , c= 9 kN/m2 , ∅= 360 , Nc = 52, Nq = 35 and Nγ = 42. [8+8] 2. (a) Differentiate between ‘initial settlement’ and ‘consolidation settlement’ bringing out clearly where do you expect each of them to occur. (b) A plan of a proposed heap is shown in Figure 2. The heap will stand on a thick deposit soft clay with E-value of 15kN/m2 . The uniform pressure on the soil may be assumed as 150kN/m2 . Estimate the immediate settlement under the point marked X at the surface of the soil. [8+8]

Figure 2 3. (a) Discuss the elastic settlement of pile groups in sandy soils. (b) What inputs are required for the estimation of settlement of a group of friction piles in clay? Mention the assumptions made. [8+8] 4. (a) What is downward drag force? How to determine the downward drag force of piles? (b) A bored pile with enlarged base is to be installed in a stiff clay, the undrained shear strength at base level being 220 kN/m2 . The saturated unit weight of the clay is 21 kN/m3 . The diameters of the pile shaft and base are 1.0m and 3.0m respectively. The pile extends from a depth of 4m to a depth of 22m, the top of the under-ream being at a depth of 20m. Past experience indicates that a skin friction coefficient of 0.70 is appropriate for the clay. Compute the allowable load on the pile to ensure 1 of 2

Set No. 2

Code No: RR420101

i. an overall load factor of 2, and ii. a load factor of 3 under the base, when shaft resistance is fully mobilized. [6+10] 5. Briefly discuss the simple stability analysis method of foundation wells, which are heavy enough to rotate about the base, and are rectangular in shape. Write down the equations which will help in determining the maximum and minimum base pressure as well as the maximum horizontal thrust from the bridge deck from a height ‘H’ above the maximum scour level. The grip length may be taken as ‘D’, and allowable deflection of well at maximum scour level= δ. Suitable notations may be adopted for indicating the soil and well parameters. [16] 6. Design an anchored bulkhead to support backfill of 6 m height above the level of dredge line. Both the soils below the dredge line as well as in the backfill are granular, having G= 2.7, e= 0.8 and ∅ = 300 . The ground water table is at a height of 3.5 m above the dredge line. Assume that (a) the anchor rod is at a depth of 1.5 m from the top of the backfill, (b) the desired factor of safety is 2.0.

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7. (a) What is heave? How to predict the heave of soil from oedometer test? (b) Discuss the Engineering properties of expansive soils. 8. Discuss the various foundation practices used in expansive soils. ⋆⋆⋆⋆⋆

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[8+8] [16]

Set No. 3

Code No: RR420101

IV B.Tech II Semester Regular Examinations, Apr/May 2007 ADVANCED FOUNDATION ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Draw the bearing pressure diagram for an isolated footing under i. ii. iii. iv. v.

Direct axial load Eccentric axial load Inclined and eccentric axial load Axial load and moment Axial load with moments in two directions.

(b) An isolated footing of dimensions L and B metres is subjected to a load P at ex and ey from its center of gravity. If the allowable bearing capacity of the soil below is q kN/m2 find P for ex = 0 and ey = 0.2B. [10+6] 2. (a) Discuss the settlement of footings resting on soils of finite thickness. (b) A rectangular footing 3m × 2m carries a concentric load of 900 kN, and is placed at a depth of 1.0m below ground level in a deep layer of clay. The undrained elastic modulus of clay is 50 MN/m2 . The unit weight of clay is 20 kN/m3 . Calculate the immediate average elastic settlement under the load. [10+6] 3. (a) How to find out the settlement of pile groups in cohesive soils? Discuss. (b) How would you determine the ultimate loads and settlement of pile groups in sandy soils? [8+8] 4. What are the uses of under-reamed piles? Mention the various specifications of under-reamed piles? How to determine the load capacity of under-reamed pile? [16] 5. (a) Discuss the various forces acting on a well foundation? (b) A circular well foundation of 5m external diameter and steining thickness of 1 m is used as a foundation for a bridge pier in a sandy stratum. The submerged unit weight of sand is 10 kN/m3 and angle of shearing resistance is 360 . The well is subjected to a horizontal force of 500 kN and a total moment of 4500 kNm at the scour level. The depth of well below scour level is 12 m, Assuming the well be light, check the lateral stability of the well. [8+8] 6. Describe the ‘equivalent beam’ and the ‘fixed-earth support’ methods of designing anchored bulkheads. [16] 7. (a) What are the factors influencing the swell pressure of soil? 1 of 2

Set No. 3

Code No: RR420101

(b) What are the tests available to determine the swell pressure of an expansive soil and explain any one of them very clearly? [8+8] 8. (a) Explain the design and construction of under-reamed piles. (b) Briefly describe the various techniques of soil stabilization under suitable heads. [8+8] ⋆⋆⋆⋆⋆

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Set No. 4

Code No: RR420101

IV B.Tech II Semester Regular Examinations, Apr/May 2007 ADVANCED FOUNDATION ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Discuss Hansen’s bearing capacity theory? (b) A rectangular footing, with a plan area of 1.4m × 2m is to be placed at a depth of 2m below the ground surface. The footing would be subjected to a load inclined at 100 to the vertical. The subsoil is clayey, sandy silt with saturated unit weight of 18 kN/m3 , and c’= 10 kN/m2 and ∅′ = 300 . Assuming the rate of loading is such that drained condition prevails, compute the magnitude of load the footing can carry if the water table is at the base of the footing. Take F.S= 3.0. [8+8] 2. (a) Discuss the estimation of settlement of footing embedded in sand by Schmertmann’s method. (b) Determine the settlement of a 10 m square area loaded at 100 kN/m2 , placed at 1 m below the ground level in a bed of sand. Ground water level is just below the footing. The SPT values are as follows. Depth 1m to 5m 5m to 10m 10m to 20m

Average SPT 20 25 30 [8+8]

3. A group of piles has to support a vertical axial load of 2000 kN. The piles are driven into clay and have length of 10.5 m. The thickness of the clay stratum is 15 m. The clay is followed by rock. The saturated unit weight of clay is 19 kN/m3 and its cohesion is 25 kN/m2 . The clay is normally consolidated and has a liquid limit of 60%. Its specific gravity is 2.7. The water table is at the ground surface itself. Assuming the diameter of the piles as 300 mm, design a pile group. A factor of safety of 3 is required against shear failure. Compute its ultimate settlement. [16] 4. (a) What is negative skin friction and its effect? How will you estimate the negative skin friction of group of piles? (b) A square pile group of 9 piles pass through a recently filled up material of 4.5 m depth. The diameter of the pile is 300 mm and the pile spacing is 0.9 m centre-to-centre. If the unconfined compressive strength of the cohesive material is 60 kN/m2 and unit weight is 15 kN/m3 , compute the negative skin friction of the pile group. [8+8] 5. (a) Discuss the various forces acting on a well foundation? 1 of 2

Set No. 4

Code No: RR420101

(b) A circular well foundation of 5m external diameter and steining thickness of 1 m is used as a foundation for a bridge pier in a sandy stratum. The submerged unit weight of sand is 10 kN/m3 and angle of shearing resistance is 360 . The well is subjected to a horizontal force of 500 kN and a total moment of 4500 kNm at the scour level. The depth of well below scour level is 12 m, Assuming the well be light, check the lateral stability of the well. [8+8] 6. (a) Describe the equivalent beam method for the analysis of an anchored sheet pile wall. (b) An anchored bulkhead of total height 10.0 m retains cohesionless soil on either side of it. The upper ground surface is horizontal and is in level with the top of the bulkhead. The dredge level is 8.0 m below the top. The free water level is at 2.0 m below the top ground surface. Anchors are provided at 1.0 m below top. The saturated and submerged unit weights of the soil are 18.5 kN/m3 and 9 kN/m3 respectively. The angle of internal friction of the soil is 300 . Determine i. depth of embedment, ii. anchor pull and iii. maximum moment in the sheet pile.

[10+6]

7. (a) What are the factors influencing the swell pressure of soil? (b) What are the tests available to determine the swell pressure of an expansive soil and explain any one of them very clearly? [8+8] 8. (a) What is cohesive non-swelling layer? When do you use it and what are its limitations? (b) Discuss the principle and functioning of under-reamed piles and how to find out the bearing capacity of under-reamed piles. [8+8] ⋆⋆⋆⋆⋆

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